1. Field of the Invention
The present invention relates to an optical recording and reproducing apparatus for recording optical data onto a recording medium and reproducing the recorded optical data from the recording medium. More precisely, the present invention relates to an optical recording and reproducing apparatus in which a optical tape (recording tape) is used as a recording medium.
2. Description of Related Art
There are known optical recording/reproducing apparatuses which record and reproduce optical data onto and from a recording medium, such as a compact disk, video disk, or magneto-optical disk, etc.
In such known optical recording/reproducing apparatuses, the diameter of the beam incident on the recording medium is limited to a minimum value corresponding to a diffractive limit. Accordingly, the packing density, determined by the diffractive limit, is limited. Consequently, to increase the amount of data that can be recorded on the recording medium, it is necessary to increase the recording area of the recording medium. However, in practice, there is a limit to the diameter of a disk-shaped recording medium.
The use of optical tape as the recording media, which can provide a larger recording area than the disk-shaped recording media, has been proposed.
Upon recording data on and reproducing data from an optical tape, it is advisable to rotate a recording and reproducing head across the tape in order to increase the recording and reproducing speed, as is well known in conventional magnetic VTR's.
Unlike a magnetic recording and reproducing apparatus, it is necessary to move a beam on the recording medium at high speed to scan the recording medium in an optical recording and reproducing system. Also, in an optical recording and reproducing system, it is necessary to additionally provide a focusing mechanism for converging a beam onto the recording medium and a tracking mechanism for converging a beam onto a predetermined recording track of the recording medium.
In a conventional optical disk apparatus in which the optical disk rotates, it is not necessary to move an objective lens in order for the beam to be moved relative to the recording medium to perform the recording and reproducing operations. Accordingly, the objective lens can be easily moved to perform the focusing and tracking operations.
However, if a optical tape is used as the recording medium, it is necessary not only to move the optical tape, but also to move the beam across the optical tape. To move the beam, it is necessary to move the objective lens at high speed. However, since the objective lens is subject to a centrifugal force during the movement thereof at high speed, it is difficult to execute precise focusing and tracking operations by moving the objective lens, as in conventional optical disk apparatuses.
In a known multi-beam system in which a plurality of beams are formed on a recording medium to simultaneously record data on or reproduce data from a plurality of recording tracks of the recording medium, if a collimating lens is driven to carry out the focusing operation, the magnification changes, resulting in the variation of the distance between the incident beams.